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OKO 28 on150 YX


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Hello, I have a new 150 YX and I received today an OKO 28 carburetor. Before to install it I did disassembly it for deep cleaning and I had to reset the float level. The carb comes with 2 extra sets of main and idle jets but none of them have size # on it.

The bike start and idle good but doesn't rev, the best result is with the smaller jet so I assume that It is too rich. Anybody knows or has an idea about what jetting should be close to correct ?

One more, I removed the filter to lean it, it didn't help but at wide open throttle I see vapor gas getting out from the filter side, I don't have any experience on Chinese engine but it doesn't look good for me, does this carb is just a piece of garbage ?

Thank you

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I will post it tonight...in the afternoon for you guys !

The carb is the OKO 28 flat side with an extra jet on the air inlet. I have measure the main jet at way over 0.110 mm so #110 I guess (I don't have bigger pin to get closer).

I found a thread saying that OKO 28 are over main jetted and that a good starting point would be #95. I also read that it is a good carb so I begin to smile again !

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I spent hours today trying to get this bike working with no success...

I checked valve clearance and cam timing and it is ok. I tried to over lean than over rich it to figure out where I should go with no significant results. The best I get is with 48 pilot, 108 main, needle on 2nd groove (richer side) and 1.1/2 air screw out but it still doesn't rev. It does flame out and get hot like a lean engine but it doesn't work better when I jet it richer.

Spark plug is a CR7HIX, should I go with a colder one ? I see TBolt is selling a ER9EH for YX 4V Race Heads.

Ignition timing cannot be set, did anybody ever heard about wrong key position machining on these Chinese stuff ?

Thank you.

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I spent hours today trying to get this bike working with no success...

I checked valve clearance and cam timing and it is ok. I tried to over lean than over rich it to figure out where I should go with no significant results. The best I get is with 48 pilot, 108 main, needle on 2nd groove (richer side) and 1.1/2 air screw out but it still doesn't rev. It does flame out and get hot like a lean engine but it doesn't work better when I jet it richer.

Spark plug is a CR7HIX, should I go with a colder one ? I see TBolt is selling a ER9EH for YX 4V Race Heads.

Ignition timing cannot be set, did anybody ever heard about wrong key position machining on these Chinese stuff ?

Thank you.

have you completely disassembled the carb and ensured there is no dirt in any passages. I have cleaned carbs many times over before actually dislodging whatever was in passages.
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have you completely disassembled the carb and ensured there is no dirt in any passages. I have cleaned carbs many times over before actually dislodging whatever was in passages.

The carb is brand new. I removed burrs (!) than clean and blow every canalization.

I'm thinking now about checking exhaust header and valve sealing. I build this bike 4 years ago and remember now I got issue to assembly and seal the exhaust...it was a family mini endurance project but mom got pregnant and couldn't fit anymore in her leather so the bike slept 4 years.

Thanks.

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  • 2 weeks later...

Good nose, it is E'bay ! The original YX140 was too much wear out to be rebuild so I went with this one...I didn't know it doesn't exist 🙂

I didn't work on it since my last post, I confirmed that the exhaust doesn't seal at all in the head and stopped (no time).

What should be bore x stroke for a 150 and a 140 ?

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May be a stretch but do you have an aftermarket cdi on that bike? If so set the carb back to the settings you started at and try a factory one. I don't see it changing much but for 15$ its worth trying.

Thanks for the advice. I think I have already try a different CDI but I will again if sealing the exhaust doesn't fix it.

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  • 2 weeks later...
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Updates,

I finally get some times to work on this bike. I sealed the exhaust to the head cylinder (I machined a bush and weld it on the exhaust) and it is working way better now. I'm running short on main jet to finalyze the tuning but at least when I change jets It does modify the carburation.

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